The present invention relates to apparatus for purifying exhaust gases of internal combustion engines of automotive vehicles.
There are three kinds of catalytic converters, namely, a reducing catalytic converter for elimination of nitrogen oxides, an oxidizing catalytic converter for elimination of carbon monoxide and hydrocarbons, and three-way converter for reacting the three noxious elements at the same time. The converters comprise a catalyst bed comprising a pellet type catalyst element or monolithic or honeycomb catalyst element. The monolithic catalyst element has a series of longitudinally oriented passages, so that exhaust gases may flow smoothly through the catalyst element. However, there is a problem that reaction may not be sufficiently carried out to reduce each noxious component to the required level because of short residence time of the gas flow.
To remove the problem, there devices have been proposed for increasing the residence time of the gas flow in the converter, for example, devices where the discharge end portion of the exhaust pipe is deformed to restrict or diffuse the gas flow or a perforated plate is provided in front of the catalyst element to diffuse the gas flow and reduce the flow rate. However, these device have disadvantage that back pressure is increased by the restriction of the gas flow, which decreases the output of the engine.
Further, in the conventional catalytic converter, the axial line of the inlet port is arranged to make a right angle with the front plane of the catalyst element at the central portion thereof. Although the inlet port communicates the catalyst element through the cone-shaped guide duct, the exhaust gas flow cannot sufficiently diffuse up to the entire front plane of the catalyst element and hence has a tendency to collect in the central portion of the front plane. Consequently, the central portion is heated at a high temperature resulting in early damage to the portion.
Therefore, it is the object of the present invention to provide a monolithic type catalytic converter in which the exhaust gas may be diffused and slowed down without an increase in the back pressure and may flow uniformly passing through all passages of the catalyst element, thereby to effect sufficient oxidation of the noxious components.